Voltage Tuning of Microwave Magnetic Devices Using Magnetoelectric Transducers

ABSTRACT

Tunable microwave magnetic devices that provide increased performance with reduced size, weight, and cost. The disclosed microwave magnetic devices are voltage-tunable devices that include ferrite substrates. To tune the devices, the magnetic permeability of the respective ferrite substrates is varied by external, voltage-tuned, magnetic fringe fields created by one or more magnetoelectric (ME) transducers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of the priority of U.S. ProvisionalPatent Application No. 61/296,997 filed Jan. 21, 2010 entitled VOLTAGETUNING OF MICROWAVE MAGNETIC DEVICES USING MAGNETOELECTRIC TRANSDUCERS.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

FIELD OF THE INVENTION

The present application relates generally to tunable microwave magneticdevices, and more specifically to voltage tuning of such microwavemagnetic devices using magnetoelectric transducers.

BACKGROUND OF THE INVENTION

One type of microwave magnetic device that has long been recognized forits performance capabilities is the ferrite phase shifter. For example,ferrite phase shifters are known for their low insertion loss, microwavepower-handling capabilities, high reliability, and high radiationtolerance. In conventional ferrite phase shifter devices, operation istypically based on electromagnetic wave propagation in low-loss magneticmaterials, such as yttrium iron garnet (YIG) and spinel ferrites withcations of lithium, magnesium, nickel, and zinc. Further, such devicesare typically biased using permanent magnets and/or current-drivencoils.

However, conventional ferrite phase shifter devices have severaldrawbacks. For example, when such devices are biased using permanentmagnets, the size, weight, and cost of the devices can increase,especially for ferrite phase shifters that are designed to operate athigh frequencies (e.g., at or above X-band). Further, such devicesbiased using permanent magnets provide virtually no significanttunability of their operating frequencies. A degree of tunability can beachieved when the ferrite phase shifter devices are biased usingcurrent-driven coils. However, like the devices that are biased usingpermanent magnets, the devices biased using current-driven coils canalso have increased size, weight, and cost. Further, such devices biasedusing current-driven coils generally exhibit increased DC powerconsumption, and long response times (e.g., on the order ofmilliseconds) due to the relatively large inductance of the coils. Theuse of such conventional ferrite phase shifter devices has thereforegenerally been limited to applications in which low insertion loss andhigh power handling capability prevail over essentially all other designconsiderations.

In order to reduce the DC power consumption and to improve the responsetimes, some conventional ferrite phase shifter devices have incorporatedlatching-type ferrite phase shifters, which employ short current pulsesto set the phase of the devices. For example, such latching-type ferritephase shifters are typically designed using waveguide components andtoroidal-shaped ferrite cores. Further, the toroidal shape of theferrite cores provides a flux closure path, which can reduce the currentdrive requirements, and increase remnant magnetization within theferrite cores. However, such devices that incorporate latching-typeferrite phase shifters can also have increased size and weight due tothe relatively large waveguide components. The cost of fabricating suchdevices with waveguide components can also be high. Moreover, becausethe short current pulses used to set the phase of the devices typicallyprovide discrete phase settings, such devices incorporatinglatching-type ferrite phase shifters have generally been incapable ofproviding the high level of accuracy required for critical applications,such as phased array radar systems.

In the conventional ferrite phase shifter devices described above, theoperating frequencies have traditionally been tuned, when possible,using magnetic field tuning techniques, e.g., by changing the magneticfields applied to the respective devices. However, such magnetic fieldtuning of ferrite phase shifter devices can be slow, and can require aconsiderable amount of power. To avoid the drawbacks of magnetic fieldtuning, electric field tuning techniques have been employed in someconventional ferrite phase shifter devices. In such devices, a ferritelayer is typically bonded to a piezoelectric layer to form aferrite/piezoelectric composite element. Further, to tune the operatingfrequencies of such devices, an electric field is created in thecomposite element to produce, via the magnetoelectric (ME) effect, amechanical strain in the piezoelectric layer that transmits a force tothe ferrite layer. The force transmitted to the ferrite layer of thecomposite element manifests itself as an internal magnetic field thatcan change the phase shift of the electromagnetic waves propagatingthrough the ferrite layer.

However, electric field tuning of conventional ferrite phase shifterdevices also has several drawbacks. For example, for optimum results,the ferrite layer of the ferrite/piezoelectric composite elementincluded in such devices should have a large magnetostriction constant.However, ferrite materials that have low insertion loss generallyexhibit low magnetostriction. For this reason, such devices havetypically been designed to operate near the ferromagnetic resonance(FMR) frequency, where small internal magnetic fields generated via theME effect in the ferrite layer can cause large variations in themagnetic permeability of the ferrite layer, thereby facilitating tuningof the devices. However, operating such conventional ferrite phaseshifter devices near FMR can limit the bandwidth of the devices, andcause increased electromagnetic wave propagation losses.

It would therefore be desirable to have tunable microwave magneticdevices, and methods of tuning such microwave magnetic devices, thatavoid at least some of the drawbacks associated with the conventionalmicrowave magnetic devices described above.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present application, tunable microwave magneticdevices are disclosed that provide increased performance with reducedsize, weight, and cost. The presently disclosed microwave magneticdevices are voltage-tunable devices that include ferrite substrates. Totune the devices, the magnetic permeability of the respective ferritesubstrates is varied by external, voltage-tuned, magnetic fringe fieldscreated by one or more magnetoelectric (ME) transducers.

In accordance with one aspect, a voltage-tunable microwave magneticdevice includes a ferrite substrate, such as a polycrystalline yttriumiron garnet (YIG) substrate, or any other suitable ferrite substrate.For example, the microwave magnetic device can be a ferrite phaseshifter, a resonator, a delay line, a filter such as a band-pass orband-stop filter, a circulator, a limiter, an isolator, an antenna, orany other suitable microwave magnetic device. Moreover, an ME transducerfor use in tuning the microwave magnetic device includes one or morepiezoelectric layers, and one or more magnetostrictive layers. Each ofthe one or more magnetostrictive layers is bonded to at least one of theone or more piezoelectric layers. In accordance with an exemplaryaspect, the microwave magnetic device and at least one such MEtransducer can be implemented in the same device, or in separatedevices. For example, the piezoelectric layer included in the MEtransducer can be implemented using a lead magnesium niobate-leadtitanate (PMN-PT) single crystal, or any other suitable piezoelectricmaterial. Further, the magnetostrictive layer included in the MEtransducer can be implemented using Terfenol-D, or any other suitablemagnetostrictive material.

In accordance with an exemplary mode of operation, a voltage is appliedacross at least one piezoelectric layer of an ME transducer to create anelectric field that produces, via the ME effect, a mechanical strain inthe piezoelectric layer. The mechanical strain in the piezoelectriclayer transmits a force in at least one magnetostrictive layer of the MEtransducer, inducing an effective internal magnetic field within themagnetostrictive layer that varies the magnetization state of thatlayer. Such variation of the magnetization state of the magnetostrictivelayer creates an external, voltage-tuned, magnetic fringe fieldemanating from the edges of the magnetostrictive layer. In accordancewith an exemplary aspect, the magnetostrictive layer of the MEtransducer is disposed in the plane of, and in contact with, the ferritesubstrate of the microwave magnetic device. As a result, the magneticfringe field emanating from the edges of the magnetostrictive layer caneffectively penetrate the ferrite substrate, thereby varying themagnetic permeability of the ferrite substrate for tuning the microwavemagnetic device.

By applying a voltage across at least one ME transducer to create atleast one voltage-tuned magnetic fringe field emanating from the edgesof the ME transducer, and using the magnetic fringe field to tune amicrowave magnetic device, voltage tuning of such devices can beachieved with reduced DC power consumption and improved response time.Further, because the magnetic fringe field is created external to aferrite substrate typically included in the microwave magnetic device,the ferrite substrate can have low insertion loss and lowmagnetostriction. The microwave magnetic device can therefore bedesigned to operate away from the ferromagnetic resonance (FMR)frequency, thereby improving the device bandwidth and decreasingelectromagnetic wave propagation losses. Moreover, because fabricationprocesses can be employed to produce such microwave magnetic devices inminiaturized, planar form, the size, weight, and cost of such devicescan be reduced.

Other features, functions, and aspects of the invention will be evidentfrom the Drawings and/or the Detailed Description of the Invention thatfollow.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be more fully understood with reference to thefollowing Detailed Description of the Invention in conjunction with thedrawings of which:

FIG. 1 is a conceptual view of an exemplary voltage-tunable microwavemagnetic device, according to the present application;

FIG. 2 is a perspective view of another exemplary voltage-tunablemicrowave magnetic device, according to the present application;

FIG. 3 a is a perspective view of an exemplary magnetoelectric (ME)transducer that can be employed in conjunction with the voltage-tunablemicrowave magnetic device of FIG. 2;

FIG. 3 b is a graphical illustration of magnetostriction constant andmagnetization for a magnetostrictive layer included in the ME transducerof FIG. 3 a;

FIG. 3 c is a graphical illustration of magnetic fringe field as afunction of applied voltage for the ME transducer of FIG. 3 a;

FIG. 4 a is a perspective view of an exemplary meander line micro-stripferrite phase shifter that can be incorporated into the voltage-tunablemicrowave magnetic device of FIG. 2;

FIG. 4 b is a graphical illustration of simulated and measured insertionloss, and simulated and measured return loss, for the meander linemicro-strip ferrite phase shifter of FIG. 4 a;

FIG. 4 c is a graphical illustration of differential phase shift for themeander line micro-strip ferrite phase shifter of FIG. 4 a;

FIG. 5 is a graphical illustration of insertion phase as a function ofapplied electric field for the voltage-tunable microwave magnetic deviceof FIG. 2; and

FIG. 6 is a flow diagram of a method of voltage-tuning a microwavemagnetic device, according to the present application.

DETAILED DESCRIPTION OF THE INVENTION

The disclosure of U.S. Provisional Patent Application No. 61/296,997filed Jan. 21, 2010 entitled VOLTAGE TUNING OF MICROWAVE MAGNETICDEVICES USING MAGNETOELECTRIC TRANSDUCERS is incorporated herein byreference in its entirety.

Tunable microwave magnetic devices are disclosed that provide increasedperformance with reduced size, weight, and cost. The presently disclosedmicrowave magnetic devices are voltage-tunable devices that includeferrite substrates. To tune the devices, the magnetic permeability ofthe respective ferrite substrates is varied by external, voltage-tuned,magnetic fringe fields created by one or more magnetoelectric (ME)transducers.

FIG. 1 depicts a conceptual view of an illustrative embodiment of anexemplary voltage-tunable microwave magnetic device 100, in accordancewith the present application. As shown in FIG. 1, the microwave magneticdevice 100 includes a meander line micro-strip circuit 102, and an MEtransducer 104. For example, the meander line micro-strip circuit 102can be implemented as a meander line micro-strip ferrite phase shifter,or any other suitable type of meander line micro-strip circuit. Further,in one or more alternative embodiments, the circuit 102 can beimplemented as a resonator, a delay line, a filter such as a band-passor band-stop filter, a circulator, a limiter, an isolator, an antenna,or any other circuit suitable to be incorporated into such a microwavemagnetic device.

As further shown in FIG. 1, the meander line micro-strip circuit 102includes a ferrite substrate 106, and a micro-strip line 108 formed onthe ferrite substrate 106. For example, the ferrite substrate 106 can beimplemented as a polycrystalline yttrium iron garnet (YIG) substrate, orany other suitable type of substrate. Moreover, the ME transducer 104includes a piezoelectric layer 110, and a magnetostrictive layer 112mechanically coupled to the piezoelectric layer 110, thereby forming amagnetostrictive/piezoelectric composite element. For example, themagnetostrictive layer 112 can be implemented as a ferrite layer, or anyother suitable type of magnetostrictive layer.

To tune the meander line micro-strip circuit 102 of FIG. 1, a voltage,V, is applied across the piezoelectric layer 110 of the ME transducer104 to create an electric field that produces, via the ME effect, amechanical strain in the piezoelectric layer 110. The mechanical strainin the piezoelectric layer 110 transmits, in turn, a force to themagnetostrictive layer 112 of the ME transducer 104, thereby inducing aneffective internal magnetic field, H_(INT), within the magnetostrictivelayer 112 that varies the magnetization state of the magnetostrictivelayer 112. Such variation of the magnetization state of themagnetostrictive layer 112 creates an external, voltage-tuned, magneticfringe field, H_(EXT), that emanates from the edges of themagnetostrictive layer 112. The magnetic fringe field, H_(EXT),emanating from the edges of the magnetostrictive layer 112 effectivelypenetrates the ferrite substrate 106 of the meander line micro-stripcircuit 102, varying the magnetic permeability of the ferrite substrate106. In this way, the meander line micro-strip circuit 102 can be tunedusing the external magnetic fringe field, H_(EXT), created by the MEtransducer 104.

FIG. 2 depicts a perspective view of an illustrative embodiment ofanother exemplary voltage-tunable microwave magnetic device 200,according to the present application. As shown in FIG. 2, the microwavemagnetic device 200 includes a meander line micro-strip circuit 202,such as a meander line micro-strip ferrite phase shifter or any othersuitable meander line micro-strip circuit, and an ME transducer 203. Themeander line micro-strip circuit 202 includes a ferrite substrate 208,and a micro-strip line 210 formed on the ferrite substrate 208. Forexample, the ferrite substrate 208 can be implemented as a YIGsubstrate, or any other suitable type of substrate. The ME transducer203 includes a first ME transducer 204, and a second ME transducer 206.In accordance with the illustrative embodiment of FIG. 2, the MEtransducers 204, 206 can be identical to one another.

As further shown in FIG. 2, the ME transducer 204 includes twopiezoelectric layers 212, 214, and a magnetostrictive layer 216sandwiched between, and mechanically coupled to, the piezoelectriclayers 212, 214, thereby forming a first magnetostrictive/piezoelectriccomposite element. The ME transducer 204 further includes an electrode224 deposited on the exposed upper surface of the piezoelectric layer212, and an electrode 226 deposited on the exposed lower surface of thepiezoelectric layer 214. Similarly, the ME transducer 206 includes twopiezoelectric layers 218, 220, and a magnetostrictive layer 222sandwiched between, and mechanically coupled to, the piezoelectriclayers 218, 220, thereby forming a second magnetostrictive/piezoelectriccomposite element. The ME transducer 206 further includes an electrode228 deposited on the exposed upper surface of the piezoelectric layer218, and an electrode 230 deposited on the exposed lower surface of thepiezoelectric layer 220. Each of the magnetostrictive layers 216, 222 isdisposed proximate to the ferrite substrate 208 of the meander linemicro-strip circuit 202. In accordance with the illustrative embodimentof FIG. 2, each of the magnetostrictive layers 216, 222 is disposed inthe plane of, and in contact with, the ferrite substrate 208. Forexample, each of the magnetostrictive layers 216, 222 can be implementedusing Terfenol-D, or any other suitable type of magnetostrictivematerial. Moreover, each of the piezoelectric layers 212, 214, 218, 220can be implemented using lead magnesium niobate-lead titanate (PMN-PT)single crystals, or any other suitable type of piezoelectric material.

In accordance with an exemplary mode of operation, a voltage, V, isapplied across the electrodes 224, 226 of the ME transducer 204, andacross the electrodes 228, 230 of the ME transducer 206. The appliedvoltage, V, creates an electric field in each of the ME transducers 204,206 that produces, via the ME effect, a mechanical strain in thepiezoelectric layers 212, 214, and a mechanical strain in thepiezoelectric layers 218, 220. The mechanical strain in thepiezoelectric layers 212, 214 transmits a force in the magnetostrictivelayer 216 of the ME transducer 204, inducing an effective internalmagnetic field, H_(INT1), within the magnetostrictive layer 216 thatvaries the magnetization state of that layer 216. Similarly, themechanical strain in the piezoelectric layers 218, 220 transmits a forcein the magnetostrictive layer 222 of the ME transducer 206, inducing aneffective internal magnetic field, H_(INT2), within the magnetostrictivelayer 222 that varies the magnetization state of that layer 222. Suchvariation of the magnetization states of the magnetostrictive layers216, 222 creates external, voltage-tuned, magnetic fringe fieldsH_(EXT1), H_(EXT2), emanating from the edges of the magnetostrictivelayers 216, 222, respectively. Because each of the magnetostrictivelayers 216, 222 is disposed in the plane of, and in contact with, theferrite substrate 208 of the meander line micro-strip circuit 202, themagnetic fringe fields H_(EXT1), H_(EXT2), emanating from the edges ofthe magnetostrictive layers 216, 222, respectively, effectivelypenetrate the ferrite substrate 208, thereby varying the magneticpermeability of the ferrite substrate 208 for tuning the microwavemagnetic device 200.

The disclosed tunable microwave magnetic devices of the presentapplication will be further understood with reference to the followingillustrative, non-limiting examples, and FIGS. 3 a to 5. In a firstillustrative example, an exemplary ME transducer 300 is provided, asdepicted in FIG. 3 a. For example, each of the ME transducers 204, 206included in the microwave magnetic device 200 of FIG. 2 can be like theME transducer 300 of FIG. 3 a. As shown in FIG. 3 a, the ME transducer300 includes two piezoelectric layers 302, 304, and a magnetostrictivelayer 306 sandwiched between, and mechanically coupled to, thepiezoelectric layers 302, 304, thereby forming amagnetostrictive/piezoelectric composite element. The ME transducer 300further includes an electrode 308 deposited on the exposed upper surfaceof the piezoelectric layer 302, and an electrode 310 deposited on theexposed lower surface of the piezoelectric layer 304.

In this first illustrative example, the magnetostrictive layer 306 isimplemented as a slab of Terfenol-D having a length of about 15 mm, awidth of about 10 mm, and a thickness of about 1 mm. Further, each ofthe piezoelectric layers 302, 304 is implemented as a lead magnesiumniobate-lead titanate (PMN-PT) single crystal having substantially thesame dimensions as the magnetostrictive layer 306. It is noted thatTerfenol-D is a highly magnetostrictive material having a saturationmagnetostriction constant, λ, in excess of about 1500 ppm (see FIG. 3b), and a saturation magnetization, |4πM|, in excess of about 7000 G(see FIG. 3 b). It is also noted that PMN-PT is a highly piezoelectricmaterial that has a piezoelectric coefficient on the order of about 1700ppm when poled along the crystallographic <011> direction.

Each of the PMN-PT crystals corresponding to the respectivepiezoelectric layers 302, 304 (see FIG. 3 a) is cut so that the <011>poling direction is perpendicular to the plane of the respectivepiezoelectric layers 302, 304. Further, the <001> crystallographicdirection exhibiting maximum piezoelectric coefficient is disposed alongthe length of the respective piezoelectric layers 302, 304. Moreover,each of the PMN-PT crystals of the piezoelectric layers 302, 304 isbonded to the slab of Terfenol-D of the magnetostrictive layer 306 usinga cyanoacrylate-based adhesive or any other suitable type of adhesive,such that their poling directions are opposite to one another.

In addition, each of the electrodes 308, 310 is implemented using goldor any other suitable type of conductor deposited on the exposed upperand lower surfaces of the piezoelectric layers 302, 304, respectively.Further, leads (not shown) can be attached to the respective electrodes308, 310, and to the slab of Terfenol-D (i.e., the magnetostrictivelayer 306) using low temperature solder or any other suitable type ofsolder. In accordance with one or more alternative embodiments of thedisclosed tunable microwave magnetic devices, the ME transducer 300 canhave any suitable geometry, and can include any other suitablemultilayer structure and/or powder composites. Moreover, the MEtransducer 300 can be implemented using rods and spheres (not shown)embedded in a host matrix (not shown), as known to those skilled in theart, or any other suitable structural arrangement.

To evaluate the performance of the ME transducer 300, a voltage, V, isapplied across the electrodes 308, 310 of the ME transducer 300 using ahigh voltage amplifier to create an electric field in the ME transducer300, and ultimately induce, via the ME effect, an effective internalmagnetic field, H_(INT), within the magnetostrictive layer 306. Theeffective internal magnetic field, H_(INT), varies the magnetizationstate of the magnetostrictive layer 306, thereby creating an external,voltage-tuned, magnetic fringe field, H_(EXT), emanating from the edgesof the magnetostrictive layer 306. An electromagnet can be used togenerate an external magnetic biasing field, H_(BIAS) (not shown), whichis applied to the ME transducer 300 to bias the magnetostrictive layer306 near the maximum dλ/dH point. Alternatively, at least one permanentmagnet can be placed near the ME transducer 300 to generate the externalmagnetic biasing field, H_(BIAS), for biasing the magnetostrictive layer306. It is noted that the need for such external biasing components canbe avoided by designing ME transducer 300 with a high remnantmagnetization.

Having applied the voltage, V, across the electrodes 308, 310 of the MEtransducer 300, the external magnetic fringe field, H_(EXT), emanatingfrom the edges of the ME transducer 300 can be measured using, forexample, a Hall probe connected to a Gauss meter. FIG. 3 c depicts agraphical illustration of the measured magnetic fringe field, H, as afunction of the applied voltage, V, and the applied magnetic biasingfield, H_(BIAS). For example, with an applied magnetic biasing field,H_(BIAS), of about 0.3 kOe, a change in the magnetic fringe field, H, ofabout 0.1 kOe can be measured as the applied voltage, V, is increasedfrom about 0 volts to about 550 volts. Such a result demonstrates that apractical external, voltage-tuned, magnetic fringe field for use intuning a microwave magnetic device can be generated using the MEtransducer 300 of FIG. 3 a.

In a second illustrative example, an exemplary meander line micro-stripferrite phase shifter 400 is provided, as depicted in FIG. 4 a. Forexample, the meander line micro-strip circuit 202 included in themicrowave magnetic device 200 of FIG. 2 can be like the meander linemicro-strip ferrite phase shifter 400 of FIG. 4 a. As shown in FIG. 4 a,the meander line micro-strip ferrite phase shifter 400 includes aferrite substrate 402, and a micro-strip line 404 formed on the ferritesubstrate 402. For example, the meander line micro-strip ferrite phaseshifter 400 can be designed and simulated using any suitable finiteelement technique, as known to those skilled in the art. Further, bothreciprocal and non-reciprocal performance of the meander linemicro-strip ferrite phase shifter 400 can be achieved by suitablyvarying the coupling between the respective meander elements, as knownto those skilled in the art.

In this second illustrative example, the ferrite substrate 402 isimplemented using commercially available polycrystalline YIG, having asaturation magnetization of about 1780 G, and a ferromagnetic resonance(FMR) line width of about 15 Oe. It is noted that any other suitabletype of ferrite material may be employed, such as garnet, spinel, andhexagonal ferrites, to achieve operation from, for example, S band to Wband. FIG. 4 b depicts a graphical illustration of the simulatedinsertion loss, S₂₁, and the simulated return loss, S₁₁, with anexternal magnetic biasing field, H_(BIAS), of about 200 Oe. In addition,FIG. 4 c depicts a graphical illustration of the corresponding simulateddifferential phase shift, ΔΦ.

As shown in FIG. 4 c, the meander line micro-strip ferrite phase shifter400 exhibits a peak simulated differential phase shift, ΔΦ, of about210° at a design frequency of 6 GHz. As shown in FIG. 4 b, thecorresponding simulated insertion loss, |S₂₁|, and the correspondingsimulated return loss, |S₁₁|, are about 1.8 dB and 20 dB, respectively.It is noted that the value of the simulated differential phase shift,ΔΦ, can be obtained by subtracting the phase at an internal magneticfield, H_(INT), of about 0 Oe within the ferrite substrate 402, from thephase at an internal magnetic field, H_(INT), of about 100 Oe within theferrite substrate 402. It is further noted that the value of theinternal magnetic field, H_(INT), employed in the finite elementcalculations is substantially equal to the magnetic biasing field,H_(BIAS), minus the shape-dependent demagnetizing field of the ferritesubstrate 402.

To obtain an indication of measured performance of the meander linemicro-strip ferrite phase shifter 400, a prototype of the meander linemicro-strip ferrite phase shifter 400 is fabricated on a polycrystallineYIG substrate using, for example, gold electroplating and liftofflithography processes. Further, an electromagnet or at least onepermanent magnet is used to generate the external magnetic biasingfield, H_(BIAS), and a vector network analyzer (VNA) is connected to theprototype device for evaluation purposes. FIG. 4 b depicts a graphicalillustration of the measured insertion loss, S₂₁, and the measuredreturn loss, S₁₁, with a magnetic biasing field, H_(BIAS), of about 200Oe. Moreover, FIG. 4 c depicts a graphical illustration of thecorresponding measured differential phase shift, ΔΦ. As shown in FIG. 4c, a maximum measured differential phase shift of 180° is observed atabout 6.3 GHz with the magnetic biasing field, H_(BIAS), of about 200Oe, which is in general agreement with the simulated differential phaseshift of about 210° at the design frequency of 6 GHz discussed above.

In a third illustrative example, two ME transducers, each like the MEtransducer 300 of FIG. 3 a, are employed for voltage-tuning a meanderline micro-strip ferrite phase shifter, such as the meander linemicro-strip ferrite phase shifter 400 of FIG. 4 a. In this thirdillustrative example, the magnetostrictive layer of each of the two MEtransducers is implemented as a slab of Terfenol-D, and thepiezoelectric layers of each ME transducer are implemented as PMN-PTsingle crystals. Further, like the voltage-tunable microwave magneticdevice 200 of FIG. 2, the Terfenol-D slabs within the two ME transducersare aligned in the plane of, and in contact with, the ferrite substrateof the meander line micro-strip ferrite phase shifter to assureeffective penetration of the ferrite substrate by the magnetic fringefields emanating from the edges of the respective ME transducers. In oneor more alternative embodiments, one or more such ME transducers can beoperatively mounted above and/or below the meander line micro-stripferrite phase shifter. Moreover, an external magnetic biasing field,H_(BIAS), of about 200 Oe is applied to the ME transducers using anelectromagnet, or at least one permanent magnet. In addition, a voltageis applied across the ME transducers using a high voltage amplifier, anda VNA is connected to the meander line micro-strip ferrite phase shifterdevice for evaluation purposes.

FIG. 5 depicts the insertion phase, <S₂₁, of the meander linemicro-strip ferrite phase shifter device as a function of the appliedvoltage, which can be converted to electric field, E, by dividing theapplied voltage by the thickness (e.g., about 1 mm) of the PMN-PTcrystals within the ME transducers. As shown in FIG. 5, a phase shift ofabout 65° is observed as the electric field, E, is increased from about0 kV/cm to about 6 kV/cm. Such a result demonstrates that a practicalvoltage-tunable microwave magnetic device, such as a meander linemicro-strip ferrite phase shifter, can be realized using one or moreexternal ME transducers as tuning elements for the device.

In accordance with the present application, a method of voltage-tuning amicrowave magnetic device, using at least one ME transducer, isdescribed below with reference to FIG. 6. As depicted in step 602, avoltage is applied across the ME transducer, which includes at least onemagnetostrictive layer, and at least one piezoelectric layer. Inresponse to the applied voltage, an electric field is created in the MEtransducer, as depicted in step 604, producing, via the ME effect, amechanical strain in the piezoelectric layer. As depicted in step 606, aforce is transmitted in the magnetostrictive layer by the mechanicalstrain in the piezoelectric layer, inducing an effective internalmagnetic field within the magnetostrictive layer that varies themagnetization state of the magnetostrictive layer. As depicted in step608, in response to the variation in the magnetization state of themagnetostrictive layer, an external, voltage-tuned, magnetic fringefield is created, emanating from the edges of the ME transducer. Asdepicted in step 610, a ferrite substrate incorporated into themicrowave magnetic device is effectively penetrated by the externalmagnetic fringe field, thereby varying the magnetic permeability of theferrite substrate for tuning the microwave magnetic device.

Having described the above illustrative embodiments of the disclosedtunable microwave magnetic devices, it is noted that other alternativeembodiments or variations may be made/practiced. For example, in one ormore alternative embodiments, to reduce the applied voltage requirementsof the microwave magnetic devices, the thickness of the piezoelectriclayer(s) within the ME transducer(s) can be reduced. In this way,substantially the same electric field intensity can be created in the MEtransducer as previously described, but using the reduced level ofapplied voltage. It is noted that when the thickness of thepiezoelectric layer is reduced, corresponding reductions in thethicknesses of the magnetostrictive layer within the ME transducer andthe ferrite substrate within the microwave magnetic device may have tobe made to reduce demagnetizing fields, and to assure efficient magneticfringe field tuning of the device. In addition, to further reduce thedemagnetization fields and the applied voltage requirements, anysuitable thick film technology may be employed to implement the variouscomponents of the microwave magnetic device and/or the ME transducer,including, but not limited to, pulsed laser deposition, liquid phaseepitaxy, spin spray, and tape casting. Use of such thick film technologymay also provide for increased phase shifts, improved insertion lossperformance, and enhanced device miniaturization and integration withother system components.

It will be appreciated by those of ordinary skill in the art thatmodifications to and variations of the above-described tunable microwavemagnetic devices, and methods of voltage tuning such microwave magneticdevices using magnetoelectric transducers, may be made without departingfrom the inventive concepts disclosed herein. Accordingly, thisdisclosure should not be viewed as limited except as by the scope andspirit of the appended claims.

1. A tunable microwave magnetic device, comprising: a ferrite substrate;a micro-strip circuit formed on the ferrite substrate; and at least onemagnetoelectric (ME) transducer, wherein the ME transducer is operative,in response to a voltage applied across the ME transducer, to create anexternal magnetic fringe field emanating from the ME transducer, theexternal magnetic fringe field effectively penetrating the ferritesubstrate for tuning the microwave magnetic device.
 2. The device ofclaim 1 wherein the ME transducer includes one or more piezoelectriclayers, and one or more magnetostrictive layers, each of the one or moremagnetostrictive layers being bonded to at least one of the one or morepiezoelectric layers.
 3. The device of claim 2 wherein at least one ofthe one or more magnetostrictive layers is disposed in the plane of theferrite substrate.
 4. The device of claim 2 wherein at least one of theone or more magnetostrictive layers is disposed in contact with theferrite substrate.
 5. The device of claim 2 wherein the one or moremagnetostrictive layers are implemented using Terfenol-D.
 6. The deviceof claim 2 wherein the one or more piezoelectric layers are implementedusing lead magnesium niobate-lead titanate (PMN-PT) single crystal. 7.The device of claim 1 wherein the ME transducer includes twopiezoelectric layers, and a single magnetostrictive layer disposedbetween the piezoelectric layers.
 8. The device of claim 7 wherein thesingle magnetostrictive layer is mechanically coupled to each of the twopiezoelectric layers.
 9. The device of claim 7 wherein the singlemagnetostrictive layer is disposed in the plane of the ferritesubstrate.
 10. The device of claim 7 wherein the single magnetostrictivelayer is disposed in contact with the ferrite substrate.
 11. The deviceof claim 2 wherein the voltage applied across the ME transducer createsan electric field in the ME transducer, the electric field producing,via the ME effect, a mechanical strain in the one or more piezoelectriclayers, and wherein each of the one or more piezoelectric layers isoperative, in response to the mechanical strain, to transmit a force inat least one of the one or more magnetostrictive layers, therebyinducing an effective internal magnetic field within the respectivemagnetostrictive layer.
 12. The device of claim 11 wherein the effectiveinternal magnetic field within the respective magnetostrictive layervaries a magnetization state of the respective magnetostrictive layer,and wherein the respective magnetostrictive layer is operative, inresponse to the varied magnetization state, to create the externalmagnetic fringe field emanating from the ME transducer.
 13. The deviceof claim 1 wherein the ME transducer operates with a high remnantmagnetization, obviating a need for external biasing components.
 14. Thedevice of claim 1 wherein the micro-strip circuit formed on the ferritesubstrate is a meander line micro-strip circuit.
 15. The device of claim14 wherein the meander line micro-strip circuit is a meander linemicro-strip ferrite phase shifter.
 16. A method of tuning a microwavemagnetic device, comprising the steps of: disposing the microwavemagnetic device proximate to at least one magnetoelectric (ME)transducer; and applying a voltage across the ME transducer to create anexternal magnetic fringe field emanating from the ME transducer, theexternal magnetic fringe field effectively penetrating the microwavemagnetic device for tuning the microwave magnetic device.
 17. The methodof claim 16 wherein the microwave magnetic device includes a ferritesubstrate, wherein the ME transducer includes one or more piezoelectriclayers, and one or more magnetostrictive layers, each of the one or moremagnetostrictive layers being bonded to at least one of the one or morepiezoelectric layers, and wherein the disposing of the microwavemagnetic device includes disposing the microwave magnetic deviceproximate to the ME transducer such that at least one of the one or moremagnetostrictive layers of the ME transducer is in the plane of theferrite substrate.
 18. The method of claim 16 wherein the microwavemagnetic device includes a ferrite substrate, wherein the ME transducerincludes one or more piezoelectric layers, and one or moremagnetostrictive layers, each of the one or more magnetostrictive layersbeing bonded to at least one of the one or more piezoelectric layers,and wherein the disposing of the microwave magnetic device furtherincludes disposing the microwave magnetic device proximate to the MEtransducer such that at least one of the one or more magnetostrictivelayers of the ME transducer is in contact with the ferrite substrate.19. A tunable microwave magnetic device, comprising: a substrate havinga magnetic permeability; a circuit formed on the substrate; and at leastone magnetoelectric (ME) transducer, wherein the ME transducer isoperative, in response to a voltage applied across the ME transducer, tocreate an external magnetic fringe field emanating from the MEtransducer, the external magnetic fringe field varying the magneticpermeability of the substrate for tuning the microwave magnetic device.20. The device of claim 19 wherein the substrate is a ferrite substrate.